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5,743 Views
Registered: ‎07-26-2013

Can a PLL lock to incorrect frequency

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Hi,

 I just wish to know if a PLL can get locked if a clock with freequncy other than mentioned in  .CLKIN1_PERIOD attribute is supplied.

 

In simulation, if that happens it will give stop the simulation.But i wish to know expected behaviour on silicon.

 

I  have designed a pll with i/p clk of 100MHz ( .CLKIN1_PERIOD(10)).

If i supply 200MHz to it, will it/ should it lock?

 

Sachin

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Xilinx Employee
Xilinx Employee
9,158 Views
Registered: ‎07-11-2011

Hi,

 

I think the PLL will get locked if the supplied input frequency is in its VCO range for the silicon part.

But the programmed M and D values will be applied on input frequency and there by your out frequency will also get changed.

But it is always good to provide the programmed input frequency as your design timing constarints and routing will be based on the input or derived output frequencies.

 

Please check below link on relavant discussion

 

http://forums.xilinx.com/t5/General-Technical-Discussion/Does-MMCM-or-PLL-care-absolute-frequency-of-the-input-clock/td-p/362963

 

 

Hope this helps

 

 

Regards,

Vanitha

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Highlighted
Xilinx Employee
Xilinx Employee
9,159 Views
Registered: ‎07-11-2011

Hi,

 

I think the PLL will get locked if the supplied input frequency is in its VCO range for the silicon part.

But the programmed M and D values will be applied on input frequency and there by your out frequency will also get changed.

But it is always good to provide the programmed input frequency as your design timing constarints and routing will be based on the input or derived output frequencies.

 

Please check below link on relavant discussion

 

http://forums.xilinx.com/t5/General-Technical-Discussion/Does-MMCM-or-PLL-care-absolute-frequency-of-the-input-clock/td-p/362963

 

 

Hope this helps

 

 

Regards,

Vanitha

---------------------------------------------------------------------------------------------
Please do google search before posting, you may find relavant information.
Mark the post - "Accept as solution" and give kudos if information provided is helpful and reply oriented

View solution in original post